A 32-year-old woman at 34 weeks of gestation presents to the emergency department with severe preeclampsia. Her blood pressure is 168/110 mmHg, and she has significant proteinuria (4+ on dipstick) and mild headaches. She is admitted to the obstetric ward and started on magnesium sulfate, with a loading dose of 4 g intravenously over 30 minutes, followed by a maintenance dose of 2 g/hour. After 8 hours of infusion, the patient begins to report nausea and generalized weakness. You suspect magnesium toxicity. What is the earliest clinical sign of magnesium toxicity in patients receiving magnesium sulfate for preeclampsia?
